5-Iodo-2'-deoxyuridine (IdUrd) in concentrations that are minimally inhibitory to cell division, causes 3-20 fold increases in the alkaline phosphatase activity of HeLa cells. The proposed work will investigate the mechanism of this effect by IdUrd. The areas to be studied are: (1) Is the increased activity due to more enzyme synthesis or modification or existing enzyme? (2) What is the relation between enzyme induction and IdUrd substitution into DNA? (3) What role if any does cyclic AMP and related enzymes play in the inductive process? The investigation of the third area is based upon data obtained concerning alkaline phosphatase induction by glucocorticoids.